1. Field of the Invention
The invention is directed to aqueous compositions containing polymerizable components and a catalyst for the polymerization reaction sorbed onto a particulate carrier, polymers produced thereby and articles coated with said polymers. The invention also relates to water incompatible catalyst sorbed onto on an inorganic particulate carrier for aqueous coatings.
2. Description of Related Art
Catalysts are commonly used in the polymerization and crosslinking reactions of monomeric or resinous materials to form polymers. The catalysts, polymerizable components, and other additives may be in the form of coatings, particles, articles, solutions, or dispersions. The compositions may be manipulated and polymerized as “neat” compositions, i.e. in the absence of solvents or carriers, as organic solutions or as water dispersed or emulsified compositions. Each composition has it's own strengths and weaknesses.
The chemistry of the polymerizable components is the primary factor determining the type of catalyst to use, the matrix in which the reactants are manipulated is most often the determinant factor relative to the physical form of the preferred catalyst. This is especially true for water dispersed or emulsified reactants. With organic solvent systems, the catalyst is almost always readily soluble in the solvent matrix and becomes active with the application of some applied energy source, such as heat or UV. There are few problems associated with such systems as long as the chosen catalyst is soluble in the solvent matrix or polymerizable components and catalyzes the curing reaction. Insoluble but dispersible powder catalysts can be used as long as they are uniformly dispersed in the matrix, water or organic solvent, and activated only by an applied energy source. In the instance where water is used as the matrix for the dispersion or emulsification of reactants, several unique problems exist relative to the catalyst employed. When an active catalyst is incorporated into a water dispersion or emulsion, it may begin to catalyze the curing reaction prematurely. Further, the catalyst itself may adversely affect the dispersion or emulsion stability resulting in precipitation or coagulation of the organic phase. Finally, in the case of coatings, catalyst “incompatibility” may cause undesirable surface defects in the cured coating.
Many catalysts, in particular those which are soluble in the matrix, initiate catalysis of the curing reaction prematurely. Thus, the so called “pot life” or “shelf life” of the system is shortened. This means that the polymer is formed too soon and in the case of coatings, for example, may cause a number of problems such as poor adhesion of the coating to the coating substrate, poor chemical resistance, or unacceptable physical properties including pinholes, rugosity, craters, etc.
Many attempts have been made to overcome the problems of premature catalysis by developing so called “delayed action” or “latent” catalyst systems. In these systems, the catalyst is frequently absorbed into a carrier which alone or after some further treatment, acts to “bind” the catalyst and prevents it from promoting premature reaction. In these systems, some mechanism for causing the release of the catalyst from the carrier is required. For example, British Patent 899,098 teaches porous aluminum silicate having absorbed therein a curing catalyst. The polymer system is a silicone rubber. The catalyst may be dibutyltin dilaurate. As stated on page 2, lines 70 to 74. “This absorption in a molecular sieve effectively deactivates the catalyst.” Also note on page 3, lines 4 to 10 “Polar liquids, for example water, alcohol, nitrites, or similar materials may be stirred into the silicone rubber mixture and will expel the cross linking agent/and or curing catalyst from the aluminum silicate, so as so bring about vulcanization of the mixture at room temperature.” The teaching of this patent is to inactivate the catalyst by sorption onto a molecular sieve and release the catalyst with water or other polar liquid to initiate catalysis. In contrast, the present invention utilizes carriers and catalyst combinations that are stable in water.
U.S. Pat. No. 3,114,722 concerns polyurethane foam, and absorbing a water soluble amine catalyst onto shredded urethane foam to achieve delayed catalysis.
U.S. Pat. No. 3,136,731 describes a method of preparing a polyurethane with a delayed action catalyst, by sorbing the catalyst on an organic support having a density of about 0.01 to about 0.6 Kg/cm3. (See column 2, lines 7–12). The organic support is described in column 2, lines 26 to 44 as polymeric particulate materials. Organotins can be used as a catalyst—see column 6, lines 48 to 73. Polyurethane coatings are described at column 7, line 21, but apparently not water dispersed urethane coating systems. Accordingly, the teaching of the '731 patent is directed to coatings compositions which are dispersed in organic solvents, not aqueous dispersions.
U.S. Pat. No. 3,245,946 describes the use of zeolites in rubber compounding, e.g., absorbing pyrocatechol on a crystalline zeolite molecular sieve for use as a latent catalyst.
U.S. Pat. No. 3,280,0489 relates to delayed catalysis and heat activation for production of urethane foam with the major emphasis on water generating components.
U.S. Pat. No. 3,341,488 teaches the absorbing of a material into a molecular sieve and employing low molecular weight materials, such as water, to displace the catalyst from the carrier at a predetermined time under the influence of heat so that the catalyst can become active.
Published European Patent Application 0,264,834 relates to the use of polymeric micro particles on or in which catalysts (including tin catalyst) are sorbed for use in urethane coating systems, notably electrodeposited coatings including those based on blocked isocyanates. The objective of the sorbed catalyst is to achieve improved dispersion. However inorganic particulate material did not work adequately. A pigment paste, which included lead silicate and Kaolin (which is an aluminum silicate having absorptive capacity) was employed in comparative example 6. The results of testing the coatings show that comparative example #6 has poor hardness, poor chemical resistance and poor salt spray resistance, as compared to example #7. This shows that the inorganic particulates of themselves have poor curing activity. In comparison, the combination provided by the present invention of catalyst sorbed onto an inorganic carrier is effective and economical.
U.S. Pat. No. 5,177,117 describes controlled (delayed) release catalysts for production of polyurethane (foam) by using water as a blowing agent and to release the catalyst from a molecular sieve carrier. U.S. Pat. No. 3,136,731 describes the preparation of a delayed action catalyst for polyurethanes by sorbing the catalyst onto an organic support, preferably a porous bead with a density between 0.01 and 0.6 kg/cm3. The use of “delayed action” catalysts may be undesirable resulting in slower cure reactions and, in the case of coatings, poor coating quality. Furthermore, the “delayed action” catalysts which depend on water to release the catalyst from the absorbent carrier would be practically useless in a system where water is the matrix.
U.S. Pat. No. 5,218,111 describes dimerization catalyst, not coatings. It uses a sorbed phosphine catalyst.
U.S. Pat. No. 5,258,071 describes non-aqueous paint system containing vitreous particulates, e.g., glass beads to which have been affixed a bonding agent, e.g., a silane and a catalyst bonded to the glass surface through the bonding agent.
Jerabek U.S. Pat. No. 4,031,050, Jerabek et al., U.S. Pat. No. 4,017,438 and Bosso et. al. describe aqueous coating compositions based on blocked organic polyisocyanates, an amine adduct of an epoxy group-containing resin and a diorganotin catalyst. These compositions are cationic and may be electrodeposited on a cathode and are widely employed as primers for automotive substrates. In this process, a conductive article such as an auto body or an auto part is immersed in a bath of the aqueous coating and acts as an electrode in the electrodeposition process. An electric current is passed between the article and a counter-electrode in electrical contact with the aqueous coating until a desired coating thickness is deposited on the article. These coatings will be referred to herein as “E-coatings.” The present invention is particularly suited to “E-coatings.”
Chung et. al. U.S. Pat. No. 5,116,914 notes that dibutyltin oxide, which is used as a catalyst in these aqueous coatings, is difficult to disperse whereas dibutyltin dilaurate can be hydrolyzed which causes cratering problems in the deposited film. The patentees describe the use of a dibutyltin diacetyl acetonate catalyst to avoid these problems.
There are a number of problems attributed to the incompatibility of catalysts in aqueous media that have severely limited the usefulness of many catalysts. Frequently, the incorporation of catalysts into the aqueous compositions have adverse effects on the stability of dispersions or emulsions, ranging from immediate destabilization in which the organic components precipitate out to the formation of undesirable “gel” particles over time. In the instance where catalysts are insoluble solids, they are frequently difficult to disperse into the aqueous matrix. If the dispersion is insufficient, then the coating may have an uneven cure or defects, such as craters, may occur in the cured coating. Incompatibility of both insoluble solid and insoluble liquid catalysts may also have an adverse effect on storage stability, giving rise to a variety of defects in the coating, including pinholes, craters, pock marks, or an irregular surface resembling an orange peel.
The use of polymeric micro particles on or in which catalysts are sorbed are described in European Patent Application 0,264,834 as an method for achieving uniform dispersions without adversely affecting the characteristics of the cured coating. The preparation of such catalyst compositions, though add a considerable amount of processing and cost compared to processes involving the sorbing of liquid catalysts onto inorganic particulate carriers.
The need therefore exists, for an economical catalyst system and a method which can be used in water dispersed or emulsified polymerizable components without the shortcomings and limitations associated with existing catalyst systems.